1. Field of the Invention
The present invention relates to a photonic network of a multi-layered structure comprising optical paths upon optical wavelengths and electrical paths which use the optical paths.
Furthermore, the present invention relates to a path establishment method in a multi-layer photonic network, which is required for implementing cooperative operation of a high capacity photonic path network which is implemented with photonic cross connect devices, and a service network which is implemented with Layer 2/3 switches, which typically are IP routers or the like.
Furthermore, the present invention is applicable to a multi-layer photonic network which is an electrical/optical path integrated communication network. In particular, the present invention concerns the technical field of traffic engineering related to methods and procedures for establishing and releasing optical paths dynamically according to traffic quantities between sub-networks.
The present application is based upon patent applications Ser. Nos. 2002-53148, 2002-100186, 2002-133074, 2002-134091, and 2002-134459 filed in Japan, the contents of which are incorporated herein by reference.
2. Description of the Related Art
There is a per se known type of photonic network which comprises a plurality of sub-networks which perform switching and transfer by units of packets, optical transmission lines which connect these sub-networks, and nodes which terminate these optical transmission lines.
With this type of photonic network, at both ends of each of the optical wavelength links which are each made up from an optical transmission line and two of the nodes, there are respectively provided an optical wavelength switching capability (abbreviated as “LSC”) which is the capability of switching by optical wavelength units, and a packet switching capability (abbreviated as “PSC”) which is the capability of switching by packet units. Furthermore, optical wavelength links (abbreviated as “O-LSPs”) which are provided with LSC at both their ends are included in packet links (abbreviated as “E-LSPs”) which are provided with PSC at both their ends.
Since this type of photonic network possesses such a two-layered structure including both O-LSPs and E-LSPs, it is termed a multi-layer photonic network. Since when performing IP transfer of packets with this type of multi-layer photonic network, the transmission upon some intermediate paths is performed as optical signal packets by O-LSPs. Accordingly, as compared with the case of the transfer along the entire path being performed as electrical signal packets, it is possible to obtain the great variety of beneficial effects which an optical transmission line possesses, such as being able to have great transmission speed and/or multiplicity.
However, with a conventional multi-layer photonic network, the O-LSPs and the E-LSPs are managed independently, so that it is not possible to modify the O-LSPs freely according to the demand upon the E-LSPs or the traffic fluctuation.
In other words, since each of the O-LSPs operates fixedly via a common carrier leased line or the like, there are the problems that their provision cannot respond to the fluctuations of the packet traffic immediately, and that it is not possible efficiently to make the best possible use of the O-LSP resources. Furthermore there is the problem that when varying the O-LSP provision, it is necessary to make application to the photonic network administrator, and it is also necessary for the photonic network administrator to change over and establish the O-LSPs manually, and the like.
In addition although it is possible for each node to calculate a path in its own most efficient manner by every node in the photonic network having the same path establishment information, this is troublesome, because it is not necessary to advertise the information regarding a path which is established in order to respond to temporary increase in traffic, to all of the nodes.
And, as described above, a photonic network is constructed using an optical transmission line and nodes which terminate this optical transmission line.
In these nodes, there is a PSC in which the optical signal packets which are transferred upon this optical transmission line are temporarily converted into electrical signal packets and their header information is read in, and they are again converted back into optical signal packets of the optical wavelengths which correspond to their destination paths and are transferred, and also there is an LSC in which transfer of the optical signal packets which are transferred upon the optical transmission line is performed based upon the optical wavelengths of the optical signals just as they are.
Furthermore, normally, a plurality of sub-networks are connected to the photonic network, and these sub-networks are mutually interconnected by electrical paths.
These electrical paths include one or a plurality of optical paths belonging to the photonic network.
However, with a conventional photonic network, the optical paths and the electrical paths are managed independently, and it has not been possible freely to vary the optical paths according to the demand for the electrical paths or the fluctuations of traffic or the like.
Furthermore, since the optical paths have been fixedly established, there have been the problems that it has not been possible to respond to the fluctuations in packet traffic immediately, and that it has not been possible efficiently to make best use of the optical path resources.
Yet further there has been the problem that, when changing an optical path, it is necessary to make application to the photonic network administrator, and for the photonic network administrator to change over the optical path manually, so that the working efficiency has been bad.
And, due to the increase in recent years of data communication traffic such as the Internet and the like, node devices have progressively been introduced which at the present have a throughput in the Tbit/sec range, and it is anticipated that in the near future the next generation of devices will have throughputs of 10 to 100 Tbits/sec or greater.
As a means for implementing a node device which possesses this order of large scale transfer capability, there is a powerful type of photonic router which operates together both packet switching (PSC: Packet Switch Capable) for processing TCP/IP packets, which is the mainstream communication protocol upon the Internet, and also photonic switching (LSC: Lambda Switch Capable) for routing an optical path (for documentation, refer to: K. Shimano, A. Imaoka, Y. Takigawa, and K.-I. Sato, Technical Digest of NFOEC 2001, vol. 1, p. 5, July 2001).
By using such a photonic router, it becomes possible more closely to cooperate a conventional type of IP network which operates by packet switching (PSC), and a high capacity photonic path network (hereinafter termed a photonic network) which operates by optical switching (LSC).
However, when operating the above described IP network and photonic network together by using a conventional node device of the type already described, there is the important aspect that the method of newly establishing an autonomous optical path should make efficient use of network resources.
And researches have recently been commenced to be performed in relation to a so-called network construction for making the subordinate network (the IP network) and the superior network (the photonic network) both operate dynamically and also autonomously and in a distributed manner, and for making them operate together; and normally, as has already been explained, the optical paths are fixed, and no scheme has as yet been implemented of establishing new optical paths dynamically while tracking packet traffic fluctuation.
As a means for constructing the above type of high capacity network, the study and development of multi-layer photonic networks has recently progressed remarkably.
FIG. 53 shows a multi-layer photonic network. The multi-layer photonic network shown in FIG. 53 comprises a photonic core network and several electrical packet switching sub-networks.
The multi-layer photonic network of FIG. 53 is a multi-layered network, in which optical paths are established over the photonic core network, while electrical path switching sub-network groups which are connected together by these optical paths constitute the overall structure of the electrical packet switching network.
The photonic core network comprises a plurality of photonic cross connects (PXCs) and a plurality of optical fiber cables which link between these PXCs. The PXCs at the boundaries between each of the electrical packet switching sub-networks and the photonic core network are mutually connected with both these networks by optical fiber links.
The optical paths by optical fiber cables are established over the photonic core network, and mutually connect together different ones of the electrical packet switching sub-networks. Information is transparently transferred between the different electrical packet switching sub-networks over these optical paths.
It is possible to change over virtually the topology of the overall electrical packet switching network according to which of the electrical packet switching networks are mutually connected together.
FIGS. 54A to 54C show a state of affairs in which it is possible to implement two types of electrical packet switching network topology (FIGS. 54B and 54C) when a single optical path network topology has been provided (FIG. 54A).
Furthermore, an explanation of the hierarchy of the optical paths and the electrical paths will be provided with reference to FIGS. 54A to 54C.
In FIGS. 54A to 54C, the optical paths are denoted by the symbol O-LSP, while the electrical paths are denoted by the symbol E-LSP. The E-LSPs are routed upon the overall electrical packet switching network which is made up from the electrical packet switching sub-networks which are mutually connected together by the O-LSPs. In the O-LSP topology pattern #1 shown in FIG. 54B, the E-LSPs are connected together in multiple hop routing.
In other words, two of the electrical packet switching sub-networks are connected together via two of the O-LSPs in series. By contrast to this, in the O-LSP topology pattern #2 shown in FIG. 54C, the E-LSPs are connected together with a single hop.
In other words, two of the electrical packet switching sub-networks are connected together via a single one of the O-LSPs.
The overall electrical packet switching network must possess a “connected” structure, in the terminology of graph theory.
In other words, although it is necessary for all of the electrical packet switching sub-networks to be mutually connected together via O-LSPs, nevertheless it is not necessary for each of the electrical packet switching sub-networks to be directly connected to each of the others by some single O-LSP; they may be connected together in multiple hop routing.
FIGS. 55A to 55C show a connected electrical packet switching network (FIG. 55B), and a non-connected electrical packet switching network (FIG. 55C).
In the connected electrical packet switching network shown in FIG. 55B it is possible for all of the four electrical packet switching sub-networks (Subnets 1 through 4) to mutually communicate via O-LSPs, but in the non-connected electrical packet switching network shown in FIG. 55C it is only possible for three of the electrical packet switching sub-networks (Subnets 1, 2, and 4) to be mutually connected together via O-LSPs, while the other one of the electrical packet switching sub-networks (Subnet 3) cannot mutually communicate with these three electrical packet switching sub-networks via any O-LSP.
Electrical packet exchange within the E-LSPs is performed according to labels by MPLS (Multi Protocol Label Switching).
The conventional type BXCQ scheme has been known as a means for solution of the dynamic optical path topology optimization problem, which is one part of the problem which the present invention seeks to address.
As documentation related to this BXCQ technique, there may be cited “The influence exerted by multi media service characteristics upon ATM-VC network structure”, by Eiji Ohki and Naoaki Yamanaka, Technical Report of IEICE, SE94-241 IN94-183, March 1995.
And, FIG. 56 shows an example in which the four electrical packet switching sub-networks shown in FIG. 53 are mutually connected together.
The electrical packet switching sub-network 1 is directly connected to the electrical packet switching sub-networks 2 and 3 by optical paths; and, similarly, the electrical packet switching sub-network 2 is connected directly to the electrical packet switching sub-networks 1 and 4 by optical paths, the electrical packet switching sub-network 3 is connected directly to the electrical packet switching sub-networks 1 and 4 by optical paths, and the electrical packet switching sub-network 4 is connected directly to the electrical packet switching sub-networks 2 and 3 by optical paths. And, for transfer of packets from the electrical packet switching sub-network 1 to the sub-network 4, it is possible for them to pursue a multiple hop path from the electrical packet switching sub-network 1 to the electrical packet switching sub-network 2 and thence to the electrical packet switching sub-network 4 by multi-hop routing; or, alternatively, they may pursue a multiple hop path from the electrical packet switching sub-network 1 to the electrical packet switching sub-network 3 and thence to the electrical packet switching sub-network 4.
FIG. 57 shows an example in which, just as in FIG. 56, the four electrical packet switching sub-networks shown in FIG. 53 are mutually connected together, but in this case optical paths are established along diagonal paths between the electrical packet switching sub-networks 1 and 4, and between the electrical packet switching sub-networks 2 and 3.
In FIG. 53 and FIG. 57, an electrical border router upon the boundary of each of the electrical packet switching sub-networks is provided with two electrical packet transmission/reception ports connected to the photonic core network.
Which of the electrical border routers should be mutually directly connected together by optical paths via the two electrical packet transmission/reception ports which are provided to these border routers, is decided according to the traffic between the various electrical packet switching sub-networks.
If the traffic along the paths shown by the diagonal lines is low, the configuration shown in FIG. 56 is the most advantageous one; while, on the contrary, if this diagonal traffic is high, then the configuration shown in FIG. 57 is the most advantageous one.
If the optical paths are established without any consideration of the quantity of the traffic, then, for example, it may be the case that no direct optical path is established between some pair of the electrical packet switching sub-networks between which the packet transfer traffic is heavy, and then a necessity may arise for such packet transfer to be performed by multiple hop routing, which may lead to occurrence of the problem of congestion arising upon the optical paths.
The mutual traffic quantities between the electrical packet switching sub-networks can be determined by counting the number of packets which flow over the E-LSPs, or by counting the number of bytes in the packets.
The mutual traffic between all of the electrical packet switching sub-networks can be expressed in the form of a matrix, and this is termed the traffic matrix.
An example of a traffic matrix is shown in FIG. 58. In this FIG. 58 example, there is shown a traffic matrix for a network which is made up of N electrical packet switching sub-networks, and the (i,j)-th component of the matrix represents the quantity of traffic between the electrical packet switching sub-networks i and j.
The traffic varies with time, so that, even after an optical path has been established for the time being, it may later become necessary dynamically to re-establish the optical path according to the current conditions.
However, it is not desirable for the work of maintaining the overall network to be unduly increased, due to the job of establishing the optical paths according to traffic fluctuations in this way being performed manually.